/*
 * Copyright (C) 2007 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */

package com.google.common.collect;

import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtIncompatible;
import com.google.errorprone.annotations.CanIgnoreReturnValue;

/**
 * Provides equivalent behavior to {@link String#intern} for other immutable types.
 *
 * @author Kevin Bourrillion
 * @since 3.0
 */
@Beta
@GwtIncompatible
public interface Interner<E> {
    /**
     * Chooses and returns the representative instance for any of a collection of instances that are
     * equal to each other. If two {@linkplain Object#equals equal} inputs are given to this method,
     * both calls will return the same instance. That is, {@code intern(a).equals(a)} always holds,
     * and {@code
     * intern(a) == intern(b)} if and only if {@code a.equals(b)}. Note that {@code intern(a)} is
     * permitted to return one instance now and a different instance later if the original interned
     * instance was garbage-collected.
     *
     * <p>
     * <b>Warning:</b> do not use with mutable objects.
     *
     * @throws NullPointerException if {@code sample} is null
     */
    @CanIgnoreReturnValue // TODO(cpovirk): Consider removing this?
    E intern(E sample);
}
